DIVERSIDADE GENÉTICA E FUNCIONAL DE RIZOBACTÉRIAS DIAZOTRÓFICAS

Abstract

Plant growth promoting rhizobacteria (PGPR) stimulate the development of their host plant, and the plant, in turn, together with the culture conditions has a significant effect on rhizospheric bacterial community structure. In this study, the diversity of cultivable bacteria associated with the rizosphere of maize inoculated with different biofertilizers and growth in different nitrogen doses was analyzed. It was also evaluated the mass spectrometry profile of the isolates and their potential to produce siderophores, protease, indole compounds, cyanide and cellulose, and to solubilize phosphate, all activities related to plant growth promotion. The seventy seven bacterial isolates obtained by the use of five different nitrogen-free media (JMV, JNFb, NFb, LGI e LGI-P) were identified by partial sequencing of the 16S rRNA gene. The biofertilizers and the nitrogen doses did not interfere in the composition of the isolated diazotrophs from maize rhizosphere. JNFb medium permitted the isolation of a greater number of individuals, and they presented the highest richness and diversity. Among the isolates, there was a predominance of β e γ-Proteobacteria classes, being Burkholderia the most abundant genus. Mass spectrometry analysis showed potential to separate well represented genus into strain, evidencing new species of the Burkholderia genus. More than half of the isolates produced siderophores (58%) and protease (50.7%); solubilize phosphate (36.2%) and approximately a quarter of them (23.1%) were able to produce cellulase. The hydrogen cyanide production showed to be rare, being detected in only 4.3% of isolates, all belonging to the genus Pseudomonas sp.. All analyzed bacteria showed at least one activity and 55% showed three or more. Principal component analysis indicated that (1) Burkholderia sp. e Luteibacter sp. genus have significant correlation (p <0,05 or p<0,001) with protease and siderophores production and phosphate solubilization, (2) Bacillus sp. and Luteibacter sp. have significant correlation with indole compounds and cellulase production and (3) Pseudomonas sp. has significant correlation with protease, cyanide, siderophores, indole compounds and cellulase production. Based on the demand for grass biofertilizers able to partially or completely replace chemical fertilizers, the isolates which have several activities that promote plant growth are promising to be used as biofertilizer. Some genus clearly they share at least three equal activities featuring redundant function among them.